Disk filter and filter disk used for same

ABSTRACT

A disk filter ( 21 ) has grooves ( 211 ) having a curved shape whose curvature gradually increases from the outer peripheral side of the filter disks ( 21 ) to the inner peripheral side thereof. The width (Wout) is greater than the width (Win). The width (Wout) is the width of an opening ( 211   a ) of each of the grooves ( 211 ), the width (Win) is the width of the opening ( 211   a ) of each of the filter disks ( 21 ). The disk filter includes, in a flow passage for liquid thereof, a stacked body composed of the filter disks ( 21 ). The pressure loss of the disk filter ( 21 ) is low and the opening ratio thereof is high. The disk filter ( 21 ) can appropriately and efficiently filtrate even a low-pressure liquid.

TECHNICAL FIELD

The present invention relates to a disk filter and a filter disk usedfor the disk filter, and in particular to a disk filter suitable forfiltration of liquid and a filter disk used for the disk filter.

BACKGROUND ART

Conventionally, a so-called disk filter has been employed to filterwater for various uses such as irrigation.

The disk filter has a configuration in which a plurality of plate-shapedannular filter disks are housed in a filter case such that the filterdisks are fitted around the outer periphery of a center shaft and arevertically stacked on one another.

The front surface and the rear surface of each filter disk are providedwith grooves extending from the outer end (outer periphery) toward theinner end (inner periphery) in the radial direction. With such grooves,water channels (water introduction paths) are defined between the grooveon the front surface of the first filter disk and the rear surface ofthe second filter disk when the first filter disk and the second filterdisk are stacking on each other, for example.

In addition, the filter case includes an inlet from which water suppliedfrom the water source enters, and an outlet from which filtered water isoutput to a supply destination (downstream side).

In the disk filter, at the time when water having entered the filtercase from the inlet flows into the channels defined by the grooves ofthe filter disks, foreign matters in the water are captured at theperipheral surfaces or channels of the filter disks, and thus the wateris filtered.

Such a disk filter is disclosed in PTL 1 for example.

However, the shape of the groove of the disk filter disclosed in PTL 1is a straight shape. Therefore, the aperture ratio on the outerperiphery side of the filter disk is smaller than the aperture ratio onthe inner periphery side of the filter disk. Here, the aperture ratio isthe ratio of the total area of all opening parts of the grooves on theouter peripheral surface or the inner periphery surface of the filterdisk, with respect to the virtual total area of the outer peripheralsurface or the inner periphery surface provided with no groove.

With such a configuration, when the water supplied to the disk filterfrom the water source side flows into the channel defined by the groovefrom the outer periphery side of the filter disk (that is, the outerperipheral surface of the filter disk is used as a surface for capturingforeign matter), the water cannot readily flow into the channel.

Accordingly, the disk filter disclosed in PTL 1 has a problem that thehydraulic pressure has to be increased by using a high pressure pump onthe water source side to appropriately perform filtration.

Examples of the method for increasing the aperture ratio on the outerperiphery side of the filter disk include, for example, a method inwhich the width of the groove is increased from the inner periphery sidetoward the outer periphery side of the filter disk, and a method inwhich the depth of the groove is increased from the inner circumferenceside toward the outer periphery side.

However, in the former method, the width of the groove graduallyincreases from the inner circumference side toward the outer peripheryside. As a result, with the former method, large foreign matters easilyenter the channel, degrading the filtration performance.

In addition, the latter method has a problem that a hole is undesirablydefined in the filter disk when the grooves on the front surface and therear surface are defined at a position where the grooves overlap eachother in the thickness direction of the filter disk.

On the other hand, PTL 2 discloses a metal filter in which a curvedgroove is provided to the surface of a metal plate member. With such afilter having the above-mentioned configuration, the aperture ratio onthe outer periphery side can be increased while avoiding theabove-mentioned two problem defect.

However, with the curved groove disclosed in PTL 2, it is difficult tolimit pressure drop (in other words, the pipe resistance of a channeldefined by a groove), in comparison with the case of a straight groove.

In particular, increase in pressure drop cannot be avoided in the casewhere the curvature change of a groove is abrupt as with groove 8cdisclosed in FIG. 10 and groove 8e disclosed in FIG. 11 in PTL 2, and inthe case where the groove is unnecessarily long as in FIG. 12 of PTL 2.

Therefore, as with the case of the disk filter having the straightgroove, the filter disclosed in PTL 2 also requires a high pressure pumpto appropriately perform filtration when the resulting pressure drop istaken into account. As described, even when the aperture ratio isincreased with the above-mentioned grooves, the pressure drop may nothave been decreased.

CITATION LIST Patent Literature

PTL 1

-   Japanese Patent Application Laid-Open No. 3-47505    PTL 2-   Japanese Patent Application Laid-Open No. 2004-181272

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a disk filter whichachieves low pressure drop, has a high aperture ratio, and can properlyand efficiently filter low pressure liquid, and to provide a filter diskused for the disk filter.

Solution to Problem

To achieve the above-described objects, the present invention providesthe disk filter described below.

[1] A disk filter including: a filter case including an inlet and anoutlet for liquid; an elongated center shaft disposed in the filtercase; and a plurality of filter disks detachably housed in the filtercase, the filter disks each having an annular plate shape and apredetermined thickness, wherein the filter disks are stacked on oneanother, with the center shaft inserted in a hole of each of the filterdisks, each filter disk includes

a plurality of grooves that connect an outer periphery and an innerperiphery of the filter disk and define a liquid channel, the groovesbeing provided on at least one of a front surface and a rear surface ofthe filter disk at a predetermined interval in a circumferentialdirection of the filter disk, each groove is defined in a curved shapewhose curvature gradually increases from the outer periphery toward theinner periphery, and a width of an opening of each groove in thecircumferential direction at the outer periphery is greater than a widthof an opening of the groove in the circumferential direction at theinner periphery.

[2] The disk filter according to [1], wherein the curved shape aclothoid curve.

[3] The disk filter according to [1], wherein the curved shape is aninvolute curve.

[4] The disk filter according to [1], wherein the curved shape is acycloid curve.

[5] The disk filter according to any one of [1] to [4], wherein eachfilter disk includes grooves provided on both of the front surface andthe rear surface, and a shape of each groove on the front surface isdifferent in plan view from a shape of each groove of the rear surface.

[6] The disk filter according to [5], wherein each groove of the frontsurface and each groove of the rear surface are so defined as to extendin one direction in the circumferential direction from the outerperiphery toward the inner periphery.

[7] A filter disk that is used for the disk filter according to any oneof [1] to [6], the filter disk having a predetermined thickness and anannular plate shape, wherein the filter disk includes a plurality ofgrooves that connect an outer periphery and an inner periphery of thefilter disk and define a liquid channel, the grooves being provided toat least one of a front surface and a rear surface of the filter disk ata predetermined interval in a circumferential direction of the filterdisk, each groove is defined in a curved shape whose curvature graduallyincreases from the outer periphery toward the inner periphery, and awidth of an opening of the each groove in the circumferential directionat the outer periphery is greater than a width of an opening of eachgroove in the circumferential direction at the inner periphery.

Advantageous Effects of Invention

Since the pressure drop of the channel is low and the aperture ratio ofthe channel is high in an embodiment of the present invention, lowpressure liquid can be properly and efficiently filtered.

With the invention according to [1], the curvature of the shape of thegroove gradually increases from the outer periphery toward the innerperiphery of the filter disk, and the width of the opening of the grooveat the outer periphery is greater than the width of the opening of thegroove at the inner periphery. Thus, the aperture ratio on the outerperiphery side of the filter disk can be increased, and increase inpressure drop due to abrupt directional change of the channel defined bythe groove can be limited.

With the invention according to [2], a moderation curve suitable formoderating the directional change of the channel in the direction fromthe outer periphery side toward the inner circumference side isselected. Thus, the pressure drop can be effectively limited.

With the invention according to [3], the pressure drop can be limited bymoderating the abrupt directional change of the channel in the directionfrom the outer periphery side toward the inner circumference side, andthe flow speed of fluid on the inner circumference side of the channelis reduced. Consequently the function of capturing foreign matters inthe groove can be enhanced.

With the invention according to [4], a moderation curve as with aclothoid curve is selected. Thus, the pressure drop can be effectivelylimited, and the flow speed of fluid in the channel can be maintained ata high speed to limit proliferation of biofilm.

With the invention according to [5], in plan view, mesh-shaped channelsdefined by the grooves that cross with one another are defined betweenadjacent two filter disks stacked on each other around the center shaft.Thus, the function of capturing foreign matters in the groove can beenhanced.

With the invention according to [6], it is possible to align thedirections of the curves of the channels that are defined by the groovesof adjacent filter disks stacked on one another in such a manner as tocross one another in plan view. Thus, even when liquid flows from thechannel defined by the groove of one of the filter disks into thechannel defined by the groove of the other of the filter disks at thecrossing points of the channels, abrupt directional change of the liquidcan be limited so as to limit the increase in pressure drop.

With the invention according to [7], it is possible to achieve a diskfilter with an increased aperture ratio that can limit pressure drop,with a simple configuration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view schematically illustrating a diskfilter according to an embodiment of the present invention;

FIG. 2 is a cross sectional view schematically illustrating a filtercartridge in the disk filter illustrated in FIG. 1;

FIG. 3 is a cross sectional view illustrating the filter cartridgeillustrated in FIG. 1 taken along line A-A in FIG. 2;

FIG. 4 is a plan view of the filter cartridge illustrated in FIG. 1;

FIG. 5 is a plan view schematically illustrating the filter disk in thedisk filter in FIG. 1;

FIG. 6 is a bottom view schematically illustrating the filter disk ofFIG. 5;

FIG. 7 is an enlarged view schematically illustrating a part of thefilter disk of FIG. 5;

FIG. 8 is an enlarged perspective view schematically illustrating a partof the filter disk of FIG. 5; and

FIG. 9 schematically illustrates a liquid channel in the disk filter ofFIG. 1.

DESCRIPTION OF EMBODIMENTS

In the following, a disk filter and a filter disk used for the diskfilter according to an embodiment of the present invention will bedescribed with reference to FIGS. 1 to 9.

FIG. 1 is a longitudinal sectional view schematically illustrating diskfilter 1 of the embodiment. FIG. 2 is a sectional view schematicallyillustrating filter cartridge 2 in disk filter 1 of FIG. 1. FIG. 3 is asectional view of filter cartridge 2 of FIG. 2 taken along line A-A.FIG. 4 is a plan view of filter cartridge 2 of FIG. 2. FIG. 5 is a planview illustrating filter disk 21 of the embodiment mounted to filtercartridge 2 in disk filter 1 of FIG. 1. FIG. 6 is a bottom view offilter disk 21 of FIG. 5.

As illustrated in FIG. 1, disk filter 1 mainly includes hollow filtercase 3, filter cartridge 2 detachably (removably) housed in filter case3, and compression spring 4 that holds filter cartridge 2 in filter case3 by the biasing force.

[Details of Configuration of Filter Case]

As illustrated in FIG. 1, filter case 3 includes upper case 31 and lowercase 32. Upper case 31 and lower case 32 may be formed of a resinmaterial such as polypropyrene.

First, upper case 31 is specifically described. As illustrated in FIG.1, upper case 31 includes outer peripheral wall 311 having a cylindricalshape, and top wall 312 continuously connected with an upper end portionof outer peripheral wall 311. Top wall 312 has a hemisphere shell shape.

As illustrated in FIG. 1, top wall 312 is provided with opening parts312 a and 312 b at left and right portions in FIG. 1, respectively.Opening parts 312 a and 312 b are respectively provided with cylindricalparts 313 and 314 that extend toward the outside of upper case 31.Cylindrical parts 313 and 314 are provided as a pair.

Of cylindrical parts 313 and 314, cylindrical part 313 shown on the leftside in FIG. 1 is inlet 313 from which liquid supplied from a liquidsupply source flows into a channel of disk filter 1. The outerperipheral surface of inlet 313 may have a screw groove for threadedlyengaging a pipe on the upstream side, which is the liquid supply sourceside. It is to be noted that examples of the liquid include water pumpedup from the water source by a pump, and mixture of water and liquidfertilizer.

On the other hand, cylindrical part 314 shown on the right side in FIG.1 is outlet 314 from which liquid having entered from inlet 313 isejected out of the channel of disk filter 1 after filtration at diskfilter 1. As illustrated in FIG. 1, outlet 314 extends also to theinside of upper case 31 from opening part 312 b. Starting end portion314 a of outlet 314 is an end portion of a part of cylindrical part 314disposed in upper case 31 which is bent downward at a right angle.Starting end portion 314 a is located at the center in upper case 31.Starting end portion 314 a functions also as a holding section thatholds filter cartridge 2 by pressing filter cartridge 2 from the upperside. An outer peripheral surface of outlet 314 on the end portion sideof (end portion outside of upper case 31) may have a screw groove forthreadedly engaging a pipe on the downstream side to which filteredliquid is supplied.

In addition, as illustrated in FIG. 1, an outer peripheral surface at alower end portion of outer peripheral wall 311 is provided with malescrew part 311 a for threadedly engaging lower case 32.

Next, lower case 32 is specifically described. As illustrated in FIG. 1,lower case 32 includes outer peripheral wall 321 having a cylindricalshape, and disk-shaped round bottom wall 322 continuously connected to alower end portion of outer peripheral wall 321. It is to be noted thatthe size of the inner diameter of outer peripheral wall 321 may be sameas that of outer peripheral wall 311 of upper case 31.

In addition, as illustrated in FIG. 1, at a center portion on the topsurface of bottom wall 322, spring receiver 323 that supportscompression spring 4 from the lower side is disposed.

Further, as illustrated in FIG. 1, the inner peripheral surface at anupper end portion of outer peripheral wall 321 is provided with femalescrew part 321 a for threadedly engaging upper case 31 with outerperipheral wall 321. It should be noted that the structure for joiningouter peripheral wall 321 to upper case 31 is not limited to theabove-described structure of the screw parts. For example, the lower endportion of upper case 31 and the upper end portion of lower case 32 maybe provided with a female screw part and a male screw part,respectively.

[Details of Configuration of Filter Cartridge]

As illustrated in FIG. 1 to FIG. 4, filter cartridge 2 includes aplurality of filter disks 21, center shaft 22, pressing flange 23, andretainer 24. Filter disks 21 are plate-shaped annular filters eachhaving a predetermined thickness. Filter disks 21 are detachably fittedaround center shaft 22. Pressing flange 23 presses filter disks 21fitted around center shaft 22 from the upper side (upper case 31 side).Retainer 24 prevents pressing flange 23 and filter disks 21 fromdropping from center shaft 22.

To be more specific, as illustrated in FIG. 1 and FIG. 2, filter disks21 are stacked along the longitudinal direction of vertically longcenter shaft 22, and disposed around the outer periphery of center shaft22. The longitudinal direction of center shaft 22 corresponds to thethickness direction of filter disks 21. Filter disks 21 may be formed ofa resin material such as polypropyrene, and in addition, may have thesame size.

In addition, as illustrated in FIG. 1 and FIG. 2, recess 221 recessedupward is formed at the lower end portion of center shaft 22.Compression spring 4 supported by spring receiver 323 is fitted inrecess 221.

Further, as illustrated in FIG. 1 and FIG. 2, annular flange part 222that outwardly protrudes in the radial direction of center shaft 22 isdisposed at the lower end portion of center shaft 22. Flange part 222supports each filter disk 21 from the lower side.

As illustrated in FIG. 1, FIG. 2 and FIG. 4, part (also referred toas“upper end part”) 22 a of center shaft 22 in a predetermined range onthe upper end side thereof has a cross shape as viewed in lateral crosssection. The outer end of upper end part 22 a in the radial direction(short direction) is located on the inner side relative to the outer endof the other portion (hereinafter referred to as “main body part”) 22 bof center shaft 22 in the short direction.

In addition, as illustrated in FIG. 3, main body part 22 b of centershaft 22 has a cross shape as viewed in lateral cross section. The crossshape of main body part 22 b is disposed at a position overlapping thecross shape of upper end part 22 a. The cross shape of main body part 22b may have a width greater than that of upper end part 22 a. Forexample, main body part 22 b may have a thickness greater than that ofupper end part 22 a, and may be more protruding from central axis ofcenter shaft 22 than upper end part 22 a. The outer diameter (or thelength of the part protruding from the central axis) of main body part22 b is slightly smaller than the inner diameter of filter disks 21 sothat filter disks 21 can be easily detached.

The above-described cross-shaped center shaft 22 defines a liquidchannel (a space in communication with outlet 314) between filter disks21 and outlet 314.

Further, as illustrated in FIG. 1 and FIG. 2, pressing flange 23includes annular small flange part 231, cylinder part 233, and annularlarge flange part 232. Cylinder part 233 is joined with small flangepart 231 at the outer peripheral edge of small flange part 231. Largeflange part 232 outwardly protrudes from the outer peripheral surface ofcylinder part 233. Small flange part 231 is joined to the innerperiphery of cylinder part 233 at the lower end thereof. Large flangepart 232 is disposed above small flange part 231. Small flange part 231,large flange part 232 and cylinder part 233 are coaxially disposed. Itshould be noted that the positional relationship between small flangepart 231 and large flange part 232 in the vertical direction may bereversed. The inner diameter of small flange part 231 is slightlygreater than the outer diameter of upper end part 22 a of center shaft22. The size of the outer diameter of small flange part 231 may be sameas that of the outer diameter of main body part 22 b of center shaft 22.In addition, the inner diameter of large flange part 232 is same as theouter diameter of small flange part 231. The outer diameter of largeflange part 232 is substantially the same as the outer diameter offilter disks 21. Further, the outer diameter of cylinder part 233 is thesame as the outer diameter of small flange part 231, and is slightlysmaller than the inner diameter of starting end portion 314 a of outlet314.

As illustrated in FIG. 1, pressing flange 23 is disposed on the outsideof upper end part 22 a of center shaft 22, and inserted to starting endportion 314 a of outlet 314. Further, pressing flange 23 presses filterdisks 21 by the biasing force of compression spring 4 transmittedthrough filter disks 21 from the lower side, so as to hold filter disks21. That is, large flange part 232 is brought into pressure contact withstarting end portion 314 a by the biasing force, and the reaction forceagainst the biasing force presses large flange part 232 against filterdisks 21.

Furthermore, as illustrated in FIG. 1 and FIG. 2, groove 22 aA forretainer 24 is defined at upper end part 22 a of center shaft 22.Retainer 24 is locked in groove 22 aA. It is to be noted that retainer24 may be the same as that disclosed in PTL 1.

Filter cartridge 2 can be housed in filter case 3 in the followingmanner. First, compression spring 4 is disposed on spring receiver 323of lower case 32. Next, filter cartridge 2 is placed in lower case 32such that compression spring 4 is fitted into recess 221 of center shaft22. Thereafter, upper case 31 is threadedly engaged with lower case 32.In the process of this thread engagement, starting end portion 314 a ofoutlet 314 makes contact with large flange part 232 while upper case 31is threadedly engaged with lower case 32. As a result, by the pressingof large flange part 232 against filter disks 21, compression spring 4is gradually pushed into spring receiver 323. Then, when filtercartridge 2 is housed by threadedly engaging upper case 31 with lowercase 32, filter disks 21 adjacent to (stacked on) each other in thethickness direction are pressed against each other by the biasing forceof compression spring 4. Thus, starting end portion 314 a of outlet 314makes tight contact with large flange part 232. As a result, inlet 313and outlet 314 are partitioned such that liquid having entered frominlet 313 cannot flow into outlet 314 without passing through a channeldefined by grooves 211 of filter disks 21 described later.

[Filter Disk]

As illustrated in FIG. 5 to FIG. 8, each filter disk 21 mounted onfilter cartridge 2 includes, at front surface 21 a and rear surface 21b, a plurality of grooves 211 for defining liquid channels extendingfrom the outer periphery side toward the inner circumference side.

Groove 211 is defined in such a manner as to extend from the outerperipheral edge to the inner peripheral edge of front surface 21 a orrear surface 21 b, and is radially disposed in a circumferentialdirection of front surface 21 a or rear surface 21 b at even intervals.

As illustrated in FIG. 7 and FIG. 8, groove 211 is defined in a shapethat extends along a predetermined curve. The shape having thepredetermined curve is a shape whose curvature gradually increases fromthe outer end side toward the inner end side. That is, groove 211 has ashape whose angle gradually changes from an angle oblique to the radialdirection of filter disks 21, to an angle in parallel with the radialdirection of filter disks 21. Groove 211 has constant width w andconstant depth d. Width w of groove 211 is the distance between bothends of groove 211 in a direction orthogonal to the curve, and depth dof groove 211 is the distance between front surface 21 a of filter disks21 and the bottom of groove 211 or between rear surface 21 b of filterdisks 21 and the bottom of groove 211. It is to be noted that the angleof groove 211 may be in parallel with the radial direction at the innerperipheral edge of filter disks 21.

As illustrated in FIG. 7 and FIG. 8, opening part 211 a on the outerperiphery side of groove 211 is provided at outer peripheral surface 21c of the cylindrical shape of filter disks 21 by cutting out outerperipheral surface 21 c. Opening part 211 b on the inner circumferenceside of groove 211 is provided at inner peripheral surface 21 d of thecylindrical shape of filter disks 21 by cutting out inner peripheralsurface 21 d.

Thus, as illustrated in FIG. 7 and FIG. 8, opening width Wout (maximumwidth of v-shaped opening part 211 a) of opening part 211 a on the outerperiphery side along the circumferential direction of filter disks 21 isgreater than opening width Win (maximum width of v-shaped opening part211 b) of opening part 211 b on the inner circumference side along theabove-mentioned circumferential direction.

As described above, in the state where filter disks 21 are brought intopressure contact with one another by the biasing force of compressionspring 4, groove 211 of one of filter disks 21 is covered by frontsurface 21 a or rear surface 21 b of adjacent filter disk 21 in thethickness direction of filter disks 21. In this manner, the liquidchannels extending from the outer periphery side toward the innercircumference side are defined between groove 211 and front surface 21 aor rear surface 21 b.

In addition, as illustrated in FIG. 7, the curvature change of groove211 of front surface 21 a extending from the outer periphery side towardthe inner circumference side of filter disks 21 is different from thecurvature change of groove 211 of rear surface 21 b. That is, in planview, the shape of groove 211 of front surface 21 a is different fromthat of rear surface 21 b. Thus, between adjacent two filter disks 21stacked on each other, mesh-shaped (or in other words, lattice-shaped)channels are defined in which groove 211 of rear surface 21 b (which isshown by the broken line in FIG. 7, for example) of one of filter disks21 and groove 211 of front surface 21 a (which is shown by the solidline in FIG. 7, for example) of the other of filter disks 21 intersectwith each other.

It is to be noted that the predetermined curve to be extended alonggroove 211 may be selected from the group consisting of clothoid curve,involute curve and cycloid curve.

In addition, as illustrated in FIG. 7, grooves 211 of front surface 21 aand groove 211 of rear surface 21 b may be defined in a shape thatextends in one direction (counterclockwise in FIG. 7) in thecircumferential direction of filter disks 21 from the outer peripheryside toward the inner circumference side of filter disk 21. That is,when the direction in which the axial angle of groove 211 with respectto the radial line of filter disk 21 gradually decreases is defined asthe direction of groove 211, the direction of groove 211 of frontsurface 21 a may be the same as that of groove 211 of rear surface 21 bin the circumferential direction of filter disks 211 (that is, clockwiseor counterclockwise). In this manner, groove 211 of front surface 21 aand groove 211 of rear surface 21 b are so defined as to extend from theouter periphery toward the inner periphery of filter disks 21 along onedirection in the circumferential direction of filter disks 21.

Further, grooves 211 of front surface 21 a and rear surface 21 b mayhave shapes extending along different portions of the same curveselected from the above-mentioned predetermined curves. Alternatively,grooves 211 of front surface 21 a and rear surface 21 b may have shapesextending along different curves (curves of the same kind havingdifferent sizes, or curves of different kinds) selected from theabove-mentioned predetermined curves.

Furthermore, while groove 211 is a V-shaped groove in FIG. 7 and in FIG.8, grooves other than the V-shaped groove may be employed as necessary.

Operation and Effect of Embodiment

In the embodiment, as indicated by the arrow in FIG. 9, liquid havingentered disk filter 1 from inlet 313 is filtered at outer peripheralsurfaces 21 c of a plurality of filter disks 21 adjacent to one another.Foreign matters in the liquid are captured at outer peripheral surfaces21 c. The liquid flows into channels defined by grooves 211 that open toouter peripheral surfaces 21 c.

Here, as illustrated in FIG. 7 and FIG. 8, opening width Wout at theouter end of groove 211 is large. Thus, even when the pressure of theliquid supplied from supply source (pump) side is low, the liquid canreadily flow into the channel.

Next, the liquid having entered the channels advances in the channelstoward inner peripheral surface 21 d of filter disks 21. In thechannels, grooves 211 form mesh-shaped channels between adjacent filterdisks 21. Thus, foreign matters that have not captured at outerperipheral surfaces 21 c are efficiently captured.

The channel is curved at a curvature which gradually changes and doesnot abruptly change the direction of the flow of the liquid. Thus, it ispossible to prevent the increase in pressure drop in the channel.

For example, when groove 211 extends along a clothoid curve, pressuredrop can be effectively limited since clothoid curves are suitable forgradually changing the direction of the channel. When groove 211 extendsalong an involute curve, pressure drop can be reduced by limiting abruptdirectional change of the channel. Further, since the flow speed on theinner circumference side of the channel decreases, the function ofcapturing foreign matters in groove 211 can be enhanced. When groove 211extends along a cycloid curve, pressure drop can be effectively limitedas with the case of the clothoid curve. When groove 211 extends along acycloid curve, the flow speed in the channel is maintained at a highspeed, and proliferation of biofilm can be limited.

Next, the liquid in the channel is ejected out of the channel throughopening part 211 b of inner peripheral surface 21 d of filter disks 21.

Then, the filtered liquid ejected out of the channel sequentially passesthrough a channel defined between filter disks 21 and main body part 22b of center shaft 22, and a channel defined between pressing flange 23and upper end part 22 a of center shaft 22, and is then ejected out ofdisk filter 1 from outlet 314.

It is to be noted that the disk filter and the filter disk according tothe embodiment of the present invention are not limited to theabove-described the embodiment, and various modifications may occur inso far as they are within the scope of the appended claims or theequivalents thereof.

For example, it is possible to provide groove 211 only to either offront surface 21 a or rear surface 21 b of filter disk 21.

It is possible to adjust the position or orientation of inlet 313 offilter case 3 such that liquid having entered from inlet 313 generates acyclone flow in filter case 3. With this configuration, liquid can flowinto the channel defined by groove 211 (on the starting end side) in thedirection substantially in parallel with the axis direction of thechannel. Thus, filtration can be promptly performed.

Further, the present invention is not limited to disk filters of thecartridge system. For example, the present invention can be applied to adisk filter in which filter disks 21 are fitted around a center shaftbuilt in a case.

This application is entitled to and claims the benefit of JapanesePatent Application No. 2012-127024 dated Jun. 4, 2012, the disclosure ofwhich including the specification, drawings and abstract is incorporatedherein by reference in its entirety.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a diskfilter which can limit pressure drop and can enhance filtrationperformance. The disk filter according to the embodiment of the presentinvention can be favorably used for filtration of low pressure liquid,such as filtration of irrigation liquid. Therefore, the presentinvention is expected to contribute to spread and develop businessesthat require transfer of low pressure liquid, such as irrigation.

REFERENCE SIGNS LIST

-   -   1 Disk filter    -   3 Filter case    -   21 Filter disk    -   21 a Front surface    -   21 b Rear surface    -   211 Groove    -   313 Inlet    -   314 Outlet

The invention claimed is:
 1. A disk filter comprising: a filter caseincluding an inlet and an outlet for liquid; an elongated center shaftdisposed in the filter case; and a plurality of filter disks detachablyhoused in the filter case, the filter disks each having an annular plateshape and a predetermined thickness, wherein the filter disks arestacked on one another, with the center shaft inserted in a holeradially-centered of each of the filter disks, each filter disk includesa plurality of grooves that connect an outer periphery and an innerperiphery of the filter disk and define a liquid channel, the groovesbeing provided on at least one of a front surface and a rear surface ofthe filter disk at a predetermined interval in a circumferentialdirection of the filter disk, each groove opens at an inner peripheraledge of the filter disk in a radial direction thereof and is defined ina curved shape whose curvature gradually increases from the outerperiphery toward the inner periphery, and a width of an opening of eachgroove in the circumferential direction at the outer periphery isgreater than a width of an opening of the groove in the circumferentialdirection at the inner periphery.
 2. The disk filter according to claim1, wherein the curved shape is a clothoid curve.
 3. The disk filteraccording to claim 1, wherein the curved shape is an involute curve. 4.The disk filter according to claim 1, wherein the curved shape is acycloid curve.
 5. The disk filter according to claim 1, wherein eachfilter disk includes grooves provided on both of the front surface andthe rear surface, and a shape of each groove on the front surface isdifferent in plan view from a shape of each groove on the rear surface.6. The disk filter according to claim 5, wherein each groove on thefront surface and each groove on the rear surface are so defined as toextend in one direction in the circumferential direction from the outerperiphery toward the inner periphery.
 7. A filter disk that is used forthe disk filter according to claim 1, the filter disk having apredetermined thickness and an annular plate shape, wherein the filterdisk includes a plurality of grooves that connect an outer periphery andan inner periphery of the filter disk and define a liquid channel, thegrooves being provided to at least one of a front surface and a rearsurface of the filter disk at a predetermined interval in acircumferential direction of the filter disk, each groove opens at aninner peripheral edge of the filter disk in a radial direction thereofand is defined in a curved shape whose curvature gradually increasesfrom the outer periphery toward the inner periphery, and a width of anopening of each of the grooves in the circumferential direction at theouter periphery is greater than a width of an opening of each of thegrooves in the circumferential direction at the inner periphery.
 8. Thedisk filter according to claim 1, wherein the inlet is configured togenerate a cyclone flow of a liquid entering from the inlet into thefilter case.